text: //===----------------------------------------------------------------------===//
  //
  // Part of the LLVM Project, under the Apache License v2.0 with LLVM Exceptions.
  // See https://llvm.org/LICENSE.txt for license information.
  // SPDX-License-Identifier: Apache-2.0 WITH LLVM-exception
  //
  //===----------------------------------------------------------------------===//
  //
  // UNSUPPORTED: libcpp-has-no-threads
  // UNSUPPORTED: c++03
  
  // <future>
  
  // class future<R>
  
  // template <class Clock, class Duration>
  //   future_status
  //   wait_until(const chrono::time_point<Clock, Duration>& abs_time) const;
  
  #include <atomic>
  #include <cassert>
  #include <chrono>
  #include <future>
  
  #include "make_test_thread.h"
  #include "test_macros.h"
  
  enum class WorkerThreadState { Uninitialized, AllowedToRun, Exiting };
  typedef std::chrono::milliseconds ms;
  
  std::atomic<WorkerThreadState> thread_state(WorkerThreadState::Uninitialized);
  
  void set_worker_thread_state(WorkerThreadState state)
  {
    thread_state.store(state, std::memory_order_relaxed);
  }
  
  void wait_for_worker_thread_state(WorkerThreadState state)
  {
    while (thread_state.load(std::memory_order_relaxed) != state)
      std::this_thread::yield();
  }
  
  void func1(std::promise<int> p)
  {
    wait_for_worker_thread_state(WorkerThreadState::AllowedToRun);
    p.set_value(3);
    set_worker_thread_state(WorkerThreadState::Exiting);
  }
  
  int j = 0;
  
  void func3(std::promise<int&> p)
  {
    wait_for_worker_thread_state(WorkerThreadState::AllowedToRun);
    j = 5;
    p.set_value(j);
    set_worker_thread_state(WorkerThreadState::Exiting);
  }
  
  void func5(std::promise<void> p)
  {
    wait_for_worker_thread_state(WorkerThreadState::AllowedToRun);
    p.set_value();
    set_worker_thread_state(WorkerThreadState::Exiting);
  }
  
  int main(int, char**)
  {
    typedef std::chrono::high_resolution_clock Clock;
    {
      typedef int T;
      std::promise<T> p;
      std::future<T> f = p.get_future();
      support::make_test_thread(func1, std::move(p)).detach();
      assert(f.valid());
      assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::timeout);
      assert(f.valid());
  
      // allow the worker thread to produce the result and wait until the worker is done
      set_worker_thread_state(WorkerThreadState::AllowedToRun);
      wait_for_worker_thread_state(WorkerThreadState::Exiting);
  
      assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::ready);
      assert(f.valid());
      f.wait();
      assert(f.valid());
    }
    {
      typedef int& T;
      std::promise<T> p;
      std::future<T> f = p.get_future();
      support::make_test_thread(func3, std::move(p)).detach();
      assert(f.valid());
      assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::timeout);
      assert(f.valid());
  
      // allow the worker thread to produce the result and wait until the worker is done
      set_worker_thread_state(WorkerThreadState::AllowedToRun);
      wait_for_worker_thread_state(WorkerThreadState::Exiting);
  
      assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::ready);
      assert(f.valid());
      f.wait();
      assert(f.valid());
    }
    {
      typedef void T;
      std::promise<T> p;
      std::future<T> f = p.get_future();
      support::make_test_thread(func5, std::move(p)).detach();
      assert(f.valid());
      assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::timeout);
      assert(f.valid());
  
      // allow the worker thread to produce the result and wait until the worker is done
      set_worker_thread_state(WorkerThreadState::AllowedToRun);
      wait_for_worker_thread_state(WorkerThreadState::Exiting);
  
      assert(f.wait_until(Clock::now() + ms(10)) == std::future_status::ready);
      assert(f.valid());
      f.wait();
      assert(f.valid());
    }
  
    return 0;
  }
  